Improving in chess

There is a lot of new information in this post.  Read it slowly and carefully.  Anytime you don't understand or have questions.   Just stop and  either message me or send me a  note.

Purpose of development - why beginners shouldn't study openings

Purpose of development -  you will learn that the purpose is to gain advantages in time, space and material by using the strategies of restraining, blockading, and executing the enemy to gain control of the center (the squares d4,d5,e4,e5).  Piece moves are direct development.  Pawn moves are aids to development, therefore they are indirect development moves.

 beginners shouldn't study openings 

Almost all strong players would disagree.  The reasons they disagree are contained in 2 books that will change your  perspective of how to play chess.  The 2 books are:  "My System" , by Aaron Nimzowitsch. and "Pawn Power In Chess", by Hans  Kmoch. 

I have learned the basic fundamentals, like develop your pieces, protect them, castle early, don't move pieces twice in a row etc.

Those  are NOT the basic fundamentals.

In order to learn  the  basic fundamentals you must change your perspective of the game of chess in 3 ways. First chess is Siege Warfare in game form.   There are 3 basic strategies in Siege Warfare.  They are:  Restrain, Blockade, and Execute the enemy. 

The  second change in perspective has to do with pawns.  The principle that you must learn is:  Winning chess is the  strategically/tactically correct advance of the pawn mass.

The 3rd change in perspective has to do with control of the center.  There are 2 theories in chess regarding control of the center:

Classical center control theory - control the center by occupying the center (d4,d5,e4,e5 squares) with pawns and pieces.

Hypermodern center control theory  - control the center with the power of your pawns and pieces.  This avoids your pawns and pieces becoming targets of the enemy pieces because they are not physically occupying the center (d4,d5,e4,e5).  

Once you learn what the basic techniques of restrain, blockade and execute the enemy are, and combine them in your brain with control the center, develop your pieces, etc. you will understand opening books. You will understand how using the strategies of restrain, blockade, and execute the enemy together with  control the center, develop your pieces, etc. combine to increase or decrease advantages/disadvantages in time, space and  material.  

The change in perspective in your brain causes you to shift your focus back and forth from concentrating on  the squares the pawns and pieces control to concentrating on the pawns and pieces  themselves as you analyze the position.  It is difficult at first to do this.  But as you practice it drastically improves your analysis of the position in front of  you. 

The second change in perspective causes you to concentrate on pawn structure.  Concentrating on pawn structure will reveal 2 things to you.  The first is the 3rd change in perspective which is what center control theory is being applied in the opening that has developed on the board.  You  will learn that there is  a difference in what moves are made if you are fighting for control of  the center with the hypermodern  method with what is called a small but secure center.  Or you are  fighting for control of  the center  with the classical method of occupying the center with your pawns and pieces.  Pawn structure is the terrain of the chess battlefield.  The second revelation is the pawn structure itself which forms the hills, valleys and  mountains of where the  war is fought.   Your plan of  attack move by move has to conform to the pawn structure,  Otherwise  your  battle plan might call for going thru a mountain given the pawn structure of the position on the board.  The bird's eye view of the  pawn structure of the position on the board makes finding candidate moves much easier.  Especially if you know  that one the important characteristics that you are looking for in the pawn structure is where the pawn breaks are or will  be in the very near future.  Pawn breaks are those places in the pawn structure where the opposing pawns are in contact with each  other in a  formation that permits captures of other pawns or pieces.  Also, the execution of a pawn break is almost always the move that signals the first move of the beginning of the middle  game.

I struggle at the next moves - the middle game - lack of plan I guess. What can I do in order to get the initiative in the middle game?

Studying  opening books teaches you the move that begins the middlegame in that opening.  Knowing the exact move when the middlegame begins is a big advantage in itself.  Studying the opening books also teaches you what typical middlegame plan(s) of attack result from the opening you are studying.  Being familiar with the typical middlegame pawn structures and where the pawn breaks are in the opening you  are  playing in a game is a great advantage over your opponent.  All of this information confirms what you wrote in your post:

I believe, that learning an opening (10-15 moves) could give you an advantage in the middle game, especially at my level, and help me have an actual plan. Am I wrong? What should I do?

What should I do? 

Select an opening repertoire that consists of 2 openings as White and 2 openings as Black(one opening against  White's 1.e4 and one opening against White's 1.d4).  Your overarching goal will be to build a visualization pattern memory bank into your brain of those openings, middlegames and endgames and the typical tactics that are themes or motifs in those 3 stages of the game.  As you are studying the openings, the middlegame, the endgame, and tactics your goal in your training is to keep adding visualization patterns to the memory bank in your brain.

I also find it difficult to apply the tactics puzzles I have sold, as there are barely any tactics that can be done, with a bad positioning.

Your chess training system should consist of  adding visualization patterns to your memory bank everyday of the following sections:

1. Tactics visualization pattern memory bank

2. Openings visualization pattern memory bank

3. Midddlegame visualization pattern memory bank

4. Endgame visualization pattern memory bank